45-year-old men that Lifetime movies have on middleaged women. It’s their leading cause of inactivity. And as if these guys don’t suffer enough, they want to scream every time they hear the same lame advice: Strengthen and stretch your lower-back and abdominal muscles. But if that’s such a good prescription, why do so many backs still ache?

Simple. Because strength and suppleness won’t help you avoid back pain. But endurance will. “Spine health isn’t about making your back muscles stronger or more flexible,” says Stuart McGill, Ph.D., a professor of spine biomechanics at the University of Waterloo in Ontario, and author of Low Back Disorders. “It’s about training them to maintain the strength they have over long periods of time.” The other critical factor, says McGill, is to “groove optimal muscle-activation patterns.” That is, teach the muscles that stabilize your spine to support your back during any activity, for maximum protection. Researchers in Finland found that men who

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lacked lower-back muscular endurance were 3.4 times more likely to develop lower-back problems than those who had fair or good endurance. That’s because poor endurance in your deep-back and abdominal muscles—the spine stabilizers with exotic-sounding names such as multifidus, quadratus lumborum, longissimus, iliocostalis, latissimus dorsi, and transverse abdominis—along with poor muscle-activation patterns, leaves you unable to sit or stand with good posture for extended periods. And poor posture increases stress on your vertebrae, turning your spine into a compacted-disk turntable, playing endless reprises of “Twist and Shout.” We asked McGill for a back-saving program, both to relieve current back pain and to reduce your chances of a future back attack. His plan: Increase...